Big Sur - Unlocking with Apple Watch

Series 5. Kept getting an error when checking “Unlock with Apple Watch.” I unpaired the  Watch and then restored from backup and it now unlocks the Mac running Big Sur and will let me approve passwords from the  Watch.

I had the same problem on MacBook Pro 15 2018 and Apple Watch Series 4. I did everything according to the instructions but it didn't work at all but maybe It had some influence on my next try.

I solved the problem by following these steps:

1) Create a new user account on your Mac.

2) Switch to a new user account and login with the same apple id as on the main account.

3) Go to the system preference and try to enable "Apple watch unlock". I had to try it two times.

4) If "Apple watch unlock" was successfully enabled you can switch to your main account. If not try to improvise or some other solution.

5) On your main account enable "Apple watch unlock". I had to try it twice and then it starts to work.

Well, the instructions suggested as much (though, I agree, not very clearly). Unpairing the Watch is the only way to force a restore from backup.

It's possible that worked out for you differently. In the past, I have had several of these Watch disconnects and yes, rebooting each device (sometimes a couple of times) sometimes got things in order, but not this time. I guess the Watch gets confused in between my MBP, my Mac Pro and the different user accounts that use the unlock feature. We'll see how long we'r good for...

+1 on this.  With bartlomiej's instructions on 11.0, watch unlock has worked reliably for the first time in over a year. I update to 11.1. Stops working again!  Infuriating! This is one of the most useful features of iWatch if you own a Mac!  

Dear Apple, I get it's complicated due to all the security hoops and Bluetooth flakiness, but c'mon! You're GD Apple! Your trademark is making complicated things easy! Don't put the feature in, if you can't make it work!

The real irony? The release notes for 11.1 lists a bug fix saying, "Unlocking Mac automatically with Apple Watch problems."

I tried the reset instructions from bartlomiej again with a couple of small tweaks (no VPN, disable unlock with watch, and skipped deleting files). Here's the modified steps (with a few less details on cert names etc).

1. VPN off. This may not be necessary, but I know there are a lot of networky things going on under the covers so I turned mine off just in case.
2. Disabled unlock with my watch in sys security preferences
3. Disable iCloud keychain sync in prefs
4. Open keychain access app
5. In the menu: view->show invisible items
6. Search for Auto Unlock (space)
7. Selected all records and deleted them. I had a really old extra one in there over what bartomiej listed. Still deleted them all.
8. Search for AutoUnlock (no space)
9. Delete all those records
10. Went into watch app on my phone and reset my watch back to factory
11. Re-paired and restored my watch from backup with the iWatch app on my phone
12. Rebooted my Mac. Did this while I waited for my watch to restore.
13. Once my watch was restored, I turned key chain sync on in iCloud sys prefs
14. Then turned on "unlock with my watch" in sys security prefs.

Notes:

When I tried to restore my watch from a backup I got obscure errors with "nul" references for both of my backups.  I reset pairing on my watch app and tried a second time. Got the latest backup to restore after another 10 minutes of waiting.

I had a couple of failures that my Mac couldn't communicate with my watch when trying to enable watch unlock in sys prefs. After a few retries it enabled and I tried logging in.  An "unlocking with watch" message showed up and then it failed. Repeat login attempt a few times.  Still failed. 

Waited a few minutes (maybe 5?). Tried again, and it seems to be working now. I'm guessing the watch was overloaded synch'ing up with my phone data and my Mac couldn't get a word in during these steps.

I don't know if it's possible to have a more un-Apple experience than this.

bartłomiej post worked for me too. macBook air 2105 with Big Sur and apple watch 4 series with wathcOS 7.1

Big thx

try bartłomiej post. it worked for me. it's a little complicated but works. at least for me it worked

Same Issue here, Mac OS Big Sur 11.0.1 (20B29) on a MacBook Pro (15-inch, 2018).

The Apple Watch is a Series 4 with WatchOS 7.1 (18R590)

Keychain Access is an application that stores passwords etc. You can access from your Launchpad in the Dock or find it in the Utilities folder on your Mac.

Doing the keychain stuff from the answers here didn't work for me. Signing out and back in to my Apple ID did: https://discussions.apple.com/thread/252033411

Complicated but it worked the second time after rebooting all my devices.

I resolved this by going into System Preferences > Security & Privacy, turn off Apple Watch unlock, restart laptop, then return to enable Apple Watch unlock. Voila ! It is working again.